fix(Interaction): allow touch highlight to affect all object materials

Previously, the touch highlighting would only change the first material
on the Interactable Object. This fix ensures that all the materials on
an object get updated by the hightlight colour.

Assets/SteamVR_Unity_Toolkit/Scripts/VRTK_InteractableObject.cs

@@ -94,7 +94,7 @@ public enum ControllerHideMode
         protected GameObject usingObject = null;
 
         private int usingState = 0;
-        private Dictionary<string, Color> originalObjectColours;
+        private Dictionary<string, Color[]> originalObjectColours;
 
         private Transform grabbedSnapHandle;
         private Transform trackPoint;
@@ -442,7 +442,7 @@ protected virtual void OnDisable()
 
         protected virtual void OnEnable()
         {
-            if(forcedDropped)
+            if (forcedDropped)
             {
                 LoadPreviousState();
             }
@@ -492,39 +492,59 @@ private Renderer[] GetRendererArray()
             return (GetComponents<Renderer>().Length > 0 ? GetComponents<Renderer>() : GetComponentsInChildren<Renderer>());
         }
 
-        private Dictionary<string, Color> StoreOriginalColors()
+        private Dictionary<string, Color[]> StoreOriginalColors()
         {
-            Dictionary<string, Color> colors = new Dictionary<string, Color>();
+            var colors = new Dictionary<string, Color[]>();
             foreach (Renderer renderer in GetRendererArray())
             {
-                if (renderer.material.HasProperty("_Color"))
+                colors[renderer.gameObject.name] = new Color[renderer.materials.Length];
+
+                for (int i = 0; i < renderer.materials.Length; i++)
                 {
-                    colors[renderer.gameObject.name] = renderer.material.color;
+                    var material = renderer.materials[i];
+                    if (material.HasProperty("_Color"))
+                    {
+                        colors[renderer.gameObject.name][i] = material.color;
+                    }
                 }
             }
             return colors;
         }
 
-        private Dictionary<string, Color> BuildHighlightColorArray(Color color)
+        private Dictionary<string, Color[]> BuildHighlightColorArray(Color color)
         {
-            Dictionary<string, Color> colors = new Dictionary<string, Color>();
+            var colors = new Dictionary<string, Color[]>();
             foreach (Renderer renderer in GetRendererArray())
             {
-                if (renderer.material.HasProperty("_Color"))
+                colors[renderer.gameObject.name] = new Color[renderer.materials.Length];
+                for (int i = 0; i < renderer.materials.Length; i++)
                 {
-                    colors[renderer.gameObject.name] = color;
+                    var material = renderer.materials[i];
+                    if (material.HasProperty("_Color"))
+                    {
+                        colors[renderer.gameObject.name][i] = color;
+                    }
                 }
             }
             return colors;
         }
 
-        private void ChangeColor(Dictionary<string, Color> colors)
+        private void ChangeColor(Dictionary<string, Color[]> colors)
         {
             foreach (Renderer renderer in GetRendererArray())
             {
-                if (renderer.material.HasProperty("_Color") && colors.ContainsKey(renderer.gameObject.name))
+                if (!colors.ContainsKey(renderer.gameObject.name))
                 {
-                    renderer.material.color = colors[renderer.gameObject.name];
+                    continue;
+                }
+
+                for (int i = 0; i < renderer.materials.Length; i++)
+                {
+                    var material = renderer.materials[i];
+                    if (material.HasProperty("_Color"))
+                    {
+                        material.color = colors[renderer.gameObject.name][i];
+                    }
                 }
             }
         }